Managing Custom ISAPI Filters

ISAPI filters are IIS applications that are used to filter requests for specific types of events, such as Read or Write. When a filter encounters an event for which it’s been configured, it responds to the event by performing a set of tasks. You can apply ISAPI filters globally or locally. Global filters affect all Web sites. Local filters affect only the currently selected Web site.

Viewing and Configuring Global Filters

Global filters affect all IIS Web sites and are loaded into memory when the World Wide Web Publishing Service is started. Anytime you add new global filters or modify existing global filters, you must stop and then restart the World Wide Web Publishing Service.

To display and configure global filters, follow these steps:

1. In the IIS snap-in, double-click the computer node for the IIS server you want to work with. Right-click Web Sites and then select Properties.

2. In the ISAPI Filters tab, you should see a list of the currently defined global filters. Global filters are active for all Web sites on the server and are executed according to priority in the order listed.

3. The summary list for filters shows the following information:

   • Status The load status of the filters. Filters that have been successfully loaded show a green up arrow. Filters that aren’t loaded show a red down arrow.

   • Filter Name The descriptive name for the filter. This name is set when you install the filter.

   • Priority The priority of the filter as set in the source code. Filters with higher priority are executed before filters with lower priority.

     Note

     You can obtain a detailed status for a filter by clicking it. The only additional information provided is the file path to the filter executable.

4. Use the following options to configure global filters:

   • Add Adds a filter. To add a new global filter, click Add. Type a filter name and then type the file path to the executable for the filter. If you don’t know the file path, click Browse and then use the Open dialog box to find the filter.

   • Remove Removes a global filter. To remove a filter, select it and then click Remove.

   • Edit Edits a global filter. The only filter property that you can edit is the executable file path. To edit a filter, select it and then click Edit. Use the Add/Edit Filter Properties dialog box provided to change the executable file path and then click OK.

5. When several filters are configured to respond to the same events, they’re executed sequentially. Filters with higher priority are executed before filters with lower priority. Filters with the same priority are executed at the global level and then at the site level. To change the execution order of a filter within a priority, use the Move Up and Move Down buttons.

6. If you’ve added or changed a global filter, you should stop and then restart the World Wide Web Publishing Service. Doing this causes IIS to load the new filters into memory.

Viewing and Configuring Local Filters

Local filters affect a single IIS Web site and can be dynamically loaded into memory when they’re added or modified, as long as the World Wide Web Publishing Service and the Web site are running. Because of this, you don’t need to stop and then restart the World Wide Web Publishing Service when you make changes to local filters.

To display and configure local filters, follow these steps:

1. In the IIS snap-in, right-click the Web site you want to manage and then choose Properties.

2. Select the ISAPI Filters tab. You should now see a list of the currently defined local filters. Local filters are active for the currently selected Web site only.

   Note

   You won’t see any global filters inherited from the Web server’s master properties. You will see only the filters installed for the currently selected Web site, even though both sets of filters are run. Although several global filters are configured by default, no local filters will exist unless an administrator has added them.

3. The summary list for filters shows the following information:

   • Status The load status of the filters. Filters that have been successfully loaded show a green up arrow. Filters that aren’t loaded show a red down arrow.

   • Filter Name The descriptive name for the filter. This name is set when you install the filter.

   • Priority The priority of the filter as set in the source code. Filters with higher priority are executed before filters with lower priority.

     Note

     You can obtain a detailed status for a filter by clicking it. The only additional information provided is the file path to the filter executable.

4. Use the following options to configure local filters:

   • Add Adds a filter. To add a new local filter, click Add. Type a filter name and then type the file path to the executable for the filter. If you don’t know the file path, click Browse and then use the Open dialog box to find the filter.

   • Remove Removes a local filter. To remove a filter, select it and then click Remove.

   • Edit Edits a local filter. The only filter property that you can edit is the executable file path. To edit a filter, select it and then click Edit. Use the Add/Edit Filter Properties dialog box provided to change the executable file path and then click OK.

5. When several filters are configured to respond to the same events, they’re executed sequentially. Filters with higher priority are executed before filters with lower priority. Filters with the same priority are executed at the global level and then at the site level. To change the execution order of a filter within a priority, use the Move Up and Move Down buttons.